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Salinity Probe Calibration
Salinity is a measurement of dissolved solids in liquid: these solids will conduct electricity to
varying degrees. A special probe is used, with two electrical contacts in it, to determine the
resistance to the flow of electricity in the liquid. The higher the resistance, the lower the PPM
of dissolved solids.
In the MkII systems, the salinity probe is located in a port on the bottom of the pump module-
manifold. This way we can look at the salinity level of the product water before deciding to
either reject the water or accept it and divert it into the holding tank.
The salinity level in parts-per-million can be seen either through the salinity meter in the soft-
ware, or on the display.
The next step is to decide what medium to use as calibration solution. If a hand-held salinity
meter is available, you can simply take a reading of your product water while the unit is run-
ning, then calibrate our MPC board to match that reading. As long as you trust the accuracy of
your hand-held meter, this is all that is necessary.
The microprocessor calculates salinity from the signals sent back to it from the probe. The
salinity circuit can be adjusted from the Spectra software by adjusting the “Salinity Calibra-
tion” parameter, or from the display in the Salinity Cal window. Increase the calibration pa-
rameter to increase the salinity reading.
Conductivity calibration solutions are available from Spectra Watermakers if another method
of calibration is necessary. These solutions are pre-made potassium chloride solutions with
known salinity levels. Calibration consists of inserting our probe into the solution and setting
the calibration parameter to the required value.
To remove the salinity probe, unplug the telephone style cable from the probe. Use a wrench
to unscrew the probe from the manifold. Re-connect the salinity probe cable, and you are
ready to calibrate. Place the flat surface of the probe containing the two metal conductivity
contacts into the calibration solution being careful not to get the cable or jacks wet. Upon re-
installation, it is recommended to use Teflon tape on the salinity probe threads before re-
installing to prevent leaks. We also recommend putting some silicone grease inside the jack, to
prevent moisture from causing corrosion inside the jack.